1. Field of the Invention
The present invention relates to a structure of a semiconductor device, and more particularly, to an edge termination of a semiconductor device having a Schottky electrode.
2. Description of the Background Art
Semiconductor devices with silicon carbide used as a base material are known for their excellent temperature characteristics and breakdown voltage characteristics. However, SiC semiconductor manufacturing technology has many difficulties to overcome, and many of them are encountered particularly in devices intended for use in high-voltage applications. For instance, one of such problems to be solved is to produce a proper edge termination around a Schottky barrier diode with SiC used as a base material. As the electric field normally reaches its peak in the vicinity of the outer edge of a Schottky electrode (hereinafter referred to as “electric field concentration”), an edge termination that can reduce the electric field concentration at and around the edge is required.
Known as an edge termination for a Schottky barrier diode formed on an SiC substrate is a Junction Termination Extension (JTE) in which the charge level of a region of p-type conductivity provided around a Schottky electrode on the SiC substrate is decreasing stepwise in an outward direction from the diode (e.g., U.S. Pat. No. 5,914,500).
In the JTE, a plurality of zones of different impurity concentrations or thicknesses need to be provided such that the charge level of the above p-type region (hereinafter referred to as a “JTE region”) is decreasing stepwise outwardly from the device. That is, the JTE region is made up of a plurality of p-type zones having different charge levels. Therefore, a great number of steps is required to form the JTE region, which contributes to interference with reduction in manufacturing costs.
As described above, the electric field concentration is likely to occur in the vicinity of the edge of a Schottky electrode. This requires proper setting of concentration and thickness of the JTE region in a position where the JTE region is in contact with the Schottky electrode; otherwise, the electric field concentration at the edge of the Schottky electrode is not sufficiently relieved, resulting in an increase in the tunneling current at the edge of the Schottky electrode, which makes it impossible to obtain a breakdown voltage close to an ideal breakdown voltage. Further, the electric field concentration also occurs at the border between a plurality of p-type zones making up the JTE region, that is, in a position where the charge level abruptly changes, which contributes to degradation in breakdown voltage characteristics of the JTE region.